DDT (dichlorodiphenyltrichloroethane) is a powerful halocarbon insecticide[1] with a controversial history. It is an extremely stable and decay-resistant chemical: the discoverer found that jars that had contained DDT and were subsequently autoclaved[2]still had enough DDT residue in them to kill insects. A little goes a long way. It's also toxic, in varying degrees, to things other than insects. It's main upsides is that it is cheap to produce and rather easy to produce huge amounts of (you can basically cook your own DDT with a high school cham lab) and that it is not immediately harmful to humans in normal doses (though it is carcinogenic in the long run). Its downsides include the development of resistances and the fact that it accumulates in fatty tissue of apex predators - like humans.

DDT use was restricted and then banned in most Western countries in the 1960s and '70s, and in those countries where it remains legal, it is only used as a health measure to control the mosquitoes that spread malaria. Only India still manufactures it. The Stockholm Convention was signed in 2001 to restrict the use of Persistent Organic Pollutants, of which DDT is the most well known (yes, DDT is organic — in the chemical sense of the word).

Carson devoted some of her book into weighing the pros and cons of DDT use,[4] but her findings did not lead to a global ban. DDT got banned in dozens of countries, but there was (and still is) no global ban on DDT; only agricultural use is almost globally banned. Places with deadly mosquito-borne illnesses still use DDT, and in some places excessive use has led to the development of DDT-resistant mosquitoes.[5][6] In fact, the drastic reduction of DDT use in agriculture delayed the onset of resistance in mosquitoes.

Not only is DDT still approved by the WHO for use against malaria (in indoor residual spraying, which is the spraying of walls of a home so a mosquito landing after it bites should get a fatal dose), but the Persistent Organic Pollutants Treaty (POPs) has a special clause for DDT.[7] Any nation may endorse the treaty calling for an end to DDT; but any nation may also use DDT at any time, for severe health reasons, by essentially writing a letter to WHO saying, "We have a health problem we think DDT may be useful to combat, so we're going to use DDT."[8]

There were several aggressive — and often successful — attempts to get rid of malaria in places where it was endemic until then.[9] Those attempts used DDT, as it was cheap and effective, and its negative effects were not yet known or understood. While there were huge successes in the 1950s, local factors, including the premature abandoning of efforts, led to a resurgence of malaria in places where it had been significantly decreased or on the brink of extinction. By the 1970s even the WHO had to admit that the program to globally eradicate malaria had failed, even though there were some remarkable successes. However, in no case was a successful eradication program stopped due to concerns regarding DDT.

Bjørn Lomborg hinted at it in his (in)famous book The Skeptical Environmentalist, but was accused by Naomi Oreskes and Eric M. Conway in their book Merchants of Doubt of using a red herring by focusing (only) on harm to humans, not environmental damage or the problem of mosquito resistance, following earlier, similar criticism from Oreskes in the journal Environmental Science & Policy.[12][13]